Many children with developmental language disorder (DLD) exhibit difficulties with phonology, i.e. the sounds of language. Children with any degree of hearing impairment (HI) are at an increased risk of problems with spoken language, including phonology. The cause of these difficulties is unknown in children with DLD, and is often assumed to result from reduced hearing acuity in children with HI. Variability in terms of language outcomes is large in both groups, and determining if a child’s language ability is within normal limits or not is problematic. A task that has proven useful in differentiating typical from atypical language development is nonword repetition, in which the child listens to a word form without meaning and repeats it back immediately. Performance in nonword repetition tasks is a potential indicator of language ability in both children with DLD and children with HI. However, it has not been established exactly what the task measures. In the present thesis, the ability to repeat prosodic and segmental features of real words and nonwords was investigated in Swedish-speaking four- to six-year-old children with DLD and HI, as well as in children with normal hearing and typical language development (TLD) (papers I, II and III). Further, relations of word and nonword repetition ability to language and hearing were explored (papers II and III), along with comparisons of phonological and grammatical production between the groups (paper IV). The findings indicated that the prosodic features stress and tonal word accent affect repetition performance in children with DLD, HI, and TLD. In general, the children with DLD and HI achieved lower results than the children with TLD on repetition of segments (consonants and vowels) and prosodic features, but tonal word accent was repeated with relatively high accuracy. Tonal word accent 1 was more accurately repeated than tonal word accent 2 by the DLD and HI children. The children with TLD repeated tonal word accent with few errors, but segments in nonwords with tonal word accent 2 were easier to repeat than segments in nonwords with tonal word accent 1. The results further revealed that the ability of children with DLD to repeat stress in real words is related to expressive grammar, but repetition of prosodic features does not reflect general language knowledge. In contrast, repetition of both segmental and prosodic nonword features may be indicative of receptive vocabulary, phonological production during naming of familiar words, and expressive grammar in children with HI. Repetition performance might be related to the degree of HI before cochlear implantation or fitting of hearing aids. Children with DLD and children with HI demonstrate similar strengths and weaknesses in phonological and grammatical production, despite the fact that they develop language under different conditions—with and without normal hearing. Tonal word accent use and syntax are relatively unimpaired in DLD and HI children. This thesis highlights prosodic and phonological strengths and weaknesses in children who have, or are at risk of, deficits in language and communication abilities. It also supports word and nonword repetition as potential predictors of some aspects of language ability in children with DLD and HI. Further, it emphasizes the importance of taking prosody into account when constructing, or interpreting results from, repetition tasks. Future research aiming to investigate the relationship between prosody in repetition and language, cognition and hearing, should use longitudinal study designs, and include younger children. Studies comparing prosodic and phonological ability in children with DLD and children with HI should employ both quantitative and qualitative analyses.